Approximately 200 adult Merino ewes at each of four sites in New Zealand, near Hamilton (Whatawhata), near Rotorua, near Havelock North (Poukawa) and near Wanganui were shorn once-yearly at five different times over two years. Groups of approximately 40 ewes in each flock were shorn pre mating (March), post mating (May), pre lambing (July) with lambs-at-foot (October) or at weaning (December/January). Midside fleece samples were collected before shearing for measurement of fibre diameter. At shearing each fleece was weighed and skirted. The skirted fleece and skirtings were weighed and core bored for measurement of wool yellowness. The between flock and between shearing time ranking for increasing wool yellowness was Wanganui, Poukawa, Rotorua, Whatawhata and lambs-at-foot, pre lambing, weaning and post mating, pre mating respectively for both the unskirted and skirted fleeces. There was a significant positive relationship between mean fibre diameter and wool yellowing with no difference in the slope of the relationship between flocks or between shearing time treatments. These trends align with finer-woolled Merino sheep having more sebaceous glands, the secretion from which appeared to protect growing wool fibres from the action of components in sweat secreted in response to warm moist atmospheric conditions. The optimal shearing time to produce the whitest wool was spring. KEYWORDS: Merino; wool yellowing; fibre diameter; shearing time.
Proceedings of the New Zealand Society of Animal Production, Volume 65, Christchurch, 191-196, 2005
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